1. Technical Field
This invention relates to devices for clamping workpieces and, more particularly, to power clamps operating under the control of reciprocal actuators to clamp and release the workpiece.
2. Discussion
Power clamps typically include a clamping arm that pivots between release and clamping positions under the control of a reciprocal actuating device such as an air cylinder. U.S. Pat. No. 4,458,889 to McPherson et al. and U.S. Pat. No. 4,021,027 to Blatt disclose known power clamps. In these designs, when the arm is in a clamping position (typically 90 degrees with respect to the axis of the cylinder piston rod) the piston rod is extended from the cylinder housing. Accordingly, the rod and associated linkage are subjected to adverse environmental conditions that are encountered when some operations are performed on the clamped workpiece. For example, power clamps are often used to weld two pieces of sheet metal. Weld flash and other debris often accompany this operation. Such debris can become lodged in the clamp head and cause poor performance and, in some instances, damage to the clamp.
The known power clamps also suffer from a variety of other disadvantages. In the above noted prior art designs the clamping arm is an integral part of the pivot linkage. As a result, it is difficult for the user to tailor the known power clamps to the user's specific operation. Many of the power clamp designs use cams or guides to create the pivoting action for the clamp arm, they use relatively small components and their rotating parts are subject to wear since there is no good provision for lubricating them. Thus, these designs are unduly complex and can lead to increases in manufacturing costs and a decrease in reliability.
Those persons knowledgeable in this art are probably aware of still other drawbacks of the prior art clamps.